1. Technical Field
The present invention relates to an unwinding device for unwinding a reel of web material, in particular a large-diameter reel for supplying web material to a processing machine located downstream of the unwinder.
Devices of this kind are used, for example, in the paper converting industry in order to supply one or more plies of paper to a rewinding machine which produces a plurality of rolls with a relatively small diameter (corresponding to the diameter of the finished rolls intended for the final user) from large-diameter reels supplied by the paper mill.
Similar unwinding devices are used in all those situations where it is required to unwind web material from a reel in order to perform various kinds of processing operations thereon.
2. State of the Art
International application WO-A-9633120 discloses an unwinder for large-diameter reels of web material, in which the reel is supported by a central spindle arranged on a carriage movable in the direction of the axis of said reel. The carriage supports two spindles so as to be able to have one reel in the working position supported by a first of the two spindles and unload the empty tubular core from the second of the two spindles and replace it with a new reel in a loading and unloading position. The two spindles supported by the carriage are in a fixed position with respect to said carriage. Unwinding of the reel is obtained by means of a series of belts driven around a plurality of pulleys, one of which is motorized and which are mounted on an oscillating arm which is brought up to the reel to be unwound, by means of an actuator. A control system for reading the reel diameter keeps the belts pressed against the external surface of the reel at an adjustable pressure in relation to the diameter of said reel. Loading and unloading of the new reel and of the empty tubular core by the carriage require a separate raising system.
Patent U.S. Pat. No. 5,730,389 describes a system for connecting together the trailing end of web material unwound from a first reel and the leading end of a new reel replacing the empty reel. In this case also unwinding of the reel is performed by means of a system of belts mounted on an oscillating arm. The belts are kept up against the external surface of the reel by means of an actuator so as to exert the pressure necessary for unwinding. The reel is supported by a spindle mounted in a fixed position on a carriage performing a displacement in the axial direction of the reel.
Further systems for unwinding reels of web material by means of belts which are mounted on arms and which are brought, from above, toward the periphery of the reels are described, for example, in EP-A-0321887, GB-B793937, DE-B-445034 and U.S. Pat. No. 1,967,056. The reel is normally mounted on a fixed spindle or on an oscillating spindle, as described in U.S. Pat. No. 1,967,056, for changing the relative position of two reels.
U.S. Pat. No. 3,202,376 describes a system of unwinding belts arranged underneath the reel which is mounted on an oscillating arm associated with a cylinder/piston actuator which presses the reel against the unwinding belts which do not have any tensioning systems.
U.S. Pat. No. 3,740,296 describes a system in which a support arm transports the reel toward a belt-type unwinding system consisting of a plurality of belts driven around pulleys mounted on an oscillating arm associated with an actuator which presses the belts against the external surface of the reel. The support arm is able to oscillate so as to remove each reel to be unwound from a carriage movable in a direction parallel to the reel axis. During unwinding, the reel support arm remains in a fixed position and the movement necessary for keeping the unwinding belts up against the reel is provided by the actuator associated with the oscillating arm on which the belt drive pulleys are mounted.
U.S. Pat. No. 2,984,426 describes an unwinding system in which an oscillating arm has the function of raising the reel from the ground and bringing it up to an unwinding system comprising belts driven around fixed pulleys. The oscillating arm gradually moves during unwinding so as to keep the reel pressed against the unwinding belts during unwinding.
The object of the present invention is to provide an unwinding system which allows optimum movement of the reels from a loading station to an unwinding station and of the empty tubular cores in the opposite direction and which also allows accurate control of the unwinding process.
A further object of the present invention is to provide a device which allows automatic unloading of the tubular core of the empty reel and automatic loading of a new reel.
The object of an improved embodiment of the invention is also to provide a device which avoids an increase in the load on the reel supports, due to the pressure between unwinding members and reel, which must be added to the weight of the reel.
The object of a further improved embodiment of the invention is to eliminate the need for inserts to be applied to the ends of the tubular core of the reel so as to allow supporting thereof during unwinding.
These and further objects and advantages, which will be clear to persons skilled in the art from reading the text which follows, are essentially obtained with a device for unwinding reels of web material comprising: a carriage movable with an alternating movement in a direction of displacement between a loading and unloading position and a position for unwinding the web material from the reel; on said carriage, at least one oscillating arm, and preferably a pair of oscillating arms for each reel, for supporting at least one reel of web material, and at least one actuator for moving the oscillating arm; in the unwinding position, a flexible unwinding member driven around a plurality of pulleys, at least one of which is motorized and at least one of which is associated with a tensioning member.
The oscillating arm is controlled by the actuator so as to gradually move the spindle of a reel to be unwound toward the flexible unwinding member in relation to the reduction in diameter of the reel. The tensioning member maintains the tension on the flexible unwinding member between an approach movement and the subsequent movement of the reel support arm or arms, with take-up of the slack.
The tensioning member may advantageously consist of an air spring, ie. a cylinder/piston system, which acts on an oscillating jockey arm carrying the respective pulleys. A sensor or a microswitch or other suitable means detects the limit position of the oscillating jockey arm, beyond which the oscillating arm and the reel mounted on it must be approached so as to restore the original position of the movable pulley.
In this way, the actuator and tensioning member control the unwinding operation so that the flexible unwinding member is always correctly pressed against the external surface of the reel.
It is also possible to envisage a system which is known per se (see WO-A-9633120) for controlling the pressure of the flexible unwinding member against the reel in relation to the diameter of the latter.
In addition to this, the actuator which performs oscillation of the oscillating arm or the oscillating arms carrying the reel also has the function of raising a new reel from a loading and unloading surface into the unwinding position and of bringing back the remainder of an unwound reel (ie. basically the tubular core around which the web material was wound) onto the loading and unloading surface.
According to a practical embodiment of the invention, the carriage supports two oscillating arms, or preferably two pairs of oscillating arms, for simultaneously handling two reels. In this way, while one arm or a pair of arms keeps the working reel in an unwinding position, the other arm or pair of arms is in the loading and unloading position and unloads the empty tubular core and removes and raises a new reel which will replace the reel temporarily being unwound after being emptied. In this case the positions for loading and unloading are two, being arranged on the two sides of a single intermediate unwinding position. In the loading and unloading positions it is also envisaged to carry out the operations for preparing the free portion of the web material of the new reel for subsequent joining to the end of the web material unwound from the working reel. This operation may be performed in the background without interfering with unwinding of the working reel.
Advantageously, the or each oscillating arm may comprise a respective expandable mandrel which is inserted into the tubular core of the reel and grips it by means of radial expansion. The need to use accessory elements to be inserted into the tubular core for supporting thereof is thus avoided.
According to a preferred embodiment of the invention, the unwinding member is located underneath the axis of the reel being unwound, so that the pressure exerted by the unwinding member on the reel is not added to the weight of said reel. The load on the support arms is thus reduced.
Further characteristic advantages and embodiments of the device and the method according to the invention are described in the accompanying claims.